The AR Workbench: A Complete Co-located Reach-in Mirror-Based ...

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Marlon Richert, Master’s Thesis, Friday, 23 February, 2007 office lighting conditions. This, however, proved to be impossible with the different shades of plastic available to us, so we settled for one that provided almost no discernible difference in perceived brightness between virtual and real objects under the dimmed lighting conditions available to us. Figure 14 The LCD video projectors. Missing from this image are the polarization filters that would sit over the lens openings. Figure 15 The motion-tracking transmitter sitting on the support beams behind the mirror sheet. Note its angle. The plastic sheet turned out to be too flexible and thus did not stay planar on its own. At the back of the sheet, this is not a problem as it rests on the support for the transmitter, but at the front, extra support is required. We achieved this by adding an extra support beam below the front of the sheet. You can see this in Figure 16. Obviously, this does impede the user’s vision somewhat, but fortunately, I designed the mirror to be somewhat oversized as to allow for a reasonable margin of error. The net effect is that the user needs to sit a little bit higher than before and bend slightly forward to look over the support beam. Finally, the execution of the workbench has some slight differences in configuration and dimension from the design. The foremost of these is that at his 30
Marlon Richert, Master’s Thesis, Friday, 23 February, 2007 discretion, the carpenter executed the support beams for the transmitter and the back of the mirror slightly differently, because of technical limitations. This, however, has no impact on the functioning of the system. Figure 16 The plastic mirror sheet of the workbench, under fully lit conditions. Under the dimmed lighting conditions required for use, it will appear significantly darker. When actually using the system, the user will need to sit a little bit higher and lean slightly forward, with their hands in front of them on the work surface. 6.2 Software At the start of each session, the user needs to register with the system so that it can properly calibrate the relative positions of the trackers, the user’s eyes and the reflection of the screen. The user first needs to place the handheld receiver squarely between their eyes and press a button on the keyboard, so the system can from there estimate the relative positions of the eyes with respect to the receiver worn on the head. After this, the screen displays a border around itself and a crosshair in its center. The user must place the handheld receiver at the two nearest corners and the center of where the screen reflection appears to be spatially located, and press a button on the keyboard each time when doing so. From this, the system calculates the relative position of the screen with respect to the transmitter. The system then uses the built-in CAVE support of IPF to take care of the stereoscopy. It simply projects what would be the front CAVE wall. The most complicated part of the software implementation is the Interaction callback structure. Figure 17 shows what is conceivably the simplest case of an Interaction callback structure in IPF that is still complete and representative of the generic case: A Interaction callback structure for a Sensor with just two pivots. Each Pivot is a point in space. The callback structure orientation ignores each Pivot’s EUL, though the application programmer can still check for this, if desired. The location DIS of each Pivot is bound to the PTO attribute of a Cond. Each Cond has an associated Region (not shown) and the STATE of a Cond is 1 when the point represented by its PTO is located inside its Region but otherwise 0 (zero). The STATEs of the two Conds feed into a FloatMultiplyMap (as there is no such thing as an IntMultiplyMap in IPF). A MapBind then tells VoidPythonMap to execute its code whenever the product of the multiplication is 1, effectively simulating a logical 31
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